1. Technical Field
The present invention relates to an integrated circuit, and more particularly, to a device and a method for preventing an integrated circuit from malfunctioning due to a surge voltage.
2. Discussion of the Related Art
An integrated circuit is an electronic circuit typically manufactured on a thin substrate of semiconductor material. As integrated circuit technology has matured, the size and operating voltages of integrated circuits and devices employing integrated circuits have decreased considerably.
Although the development of such integrated circuits has led to the proliferation of integrated circuit devices such as portable terminals, for example, cell phones and digital cameras, these devices are easily affected by suddenly applied voltages. In other words, when a surge voltage such as static electricity is applied to a portable terminal, the portable terminal may malfunction or its operability may deteriorate.
In general, a portable terminal is provided with a conductive metal on its surface to enable the portable terminal to be resistant to external forces and to be more aesthetic. A voltage of the conductive metal should not be higher than a predetermined reference voltage with respect to ground when a charged battery is attached to the portable terminal. Otherwise, a user who is carrying the portable terminal is in danger of receiving an electric shock since the conductive metal can have, for example, an alternating current (AC) voltage of about 80-90V, when it is short-circuited with the ground. Therefore, the conductive metal is typically kept in a floating state when it is not short-circuited with the ground.
However, if static electricity is applied to the conductive metal while it is in the floating state, circuit components inside the portable terminal can malfunction. In other words, when static electricity, a direct current (DC) voltage or an AC voltage are applied to or are present at the conductive metal, the performance of the portable terminal may be adversely affected.
FIG. 1A is a cross-sectional view of a general portable terminal 100.
FIG. 1B is a graph illustrating a voltage of a conductive metal on a surface of the portable terminal of FIG. 1A with respect to time.
Referring to FIG. 1A, the portable terminal 100 includes a conductive metal 110 formed on an outer surface thereof, a metal 120 for withstanding externally applied pressures, a circuit component 130 that is used to perform a function of the portable terminal 100, and a case 140.
Static electricity applied to the portable terminal 100 is discharged twice. The first discharge is referred to as a ‘first discharge’ SE1 and the second discharge is referred to as a ‘second discharge’ SE2. The first discharge SE1 indicates that the static electricity is applied to the conductive metal 110, and the second discharge SE2 indicates that the first discharge SE1 is also applied to the metal 120.
Referring now to FIG. 1B, (ii) is a waveform illustrating a voltage of the metal 120 when static electricity is applied to the metal 120. As shown by the waveform (ii), since the applied static electricity can be discharged by short-circuiting the metal 120 to ground, the voltage is not high.
However, when static electricity is applied to the conductive metal 110, a voltage of the conductive metal 110 rises as shown by a waveform (i) since the conductive metal 110 is in a floating state. In other words, the voltage of the conductive metal 110 is momentarily increased because there is no path through which the applied static electricity can be discharged, therefore increasing the possibility that the circuit component 130 will not operate properly.
Similarly, when the conductive metal 110 is connected to ground to reduce the effects of static electricity, if a DC or AC voltage is present at the conductive metal 110, the circuit component 130 may malfunction. Further, even when the static electricity is applied to the conductive metal 110, the voltage of the conductive metal 110 is similar to the waveform (ii).
As such a need exists for a technique of reducing the effects of a surge voltage on an integrated circuit device so that circuit components thereof can operate properly.